a wireless battery-less computer mouse with super capacitor energy buffer

A Wireless Battery-less Computer Mouse with Super

Capacitor Energy Buffer

A. P. Hu, Senior Member IEEE, I. L. W. Kwan, C. Tan, Y. Li

The Department of Electrical and Computer Engineering

The University of Auckland, New Zealand

Abstract-This paper proposes a novel wireless computer mouse power supply system which runs off a standard USB port and eliminates the use of batteries completely. The system uses a soft switched current-fed push-pull converter for DC to AC conversion. The AC current, which flows through a disk coil embedded into a mouse-pad, provides a time varying magnetic field that transfer power to a power pick-up coil located within the mouse, through magnetic induction. This power, which was tuned-up and regulated by an advanced voltage control method- dynamic detuning control, has proven to be able to provide sufficient power to drive a wireless mouse. Furthermore, an energy buffer system is added which backs up and allocates the induced power to allow mouse operation and energy storage to occur in a coordinated way. This system allows the mouse to sustain in operation even when it is moved away from the mouse-pad. A minimum duration of 2 minutes was achieved when the mouse was constantly active.

I. I NTRODUCTION

Inductive power transfer (IPT) systems have been developed and found many industrial applications such as materials handling systems and electric vehicles [1-3]. They utilise the principle of electromagnetic induction to achieve power transfer without galvanic contacts [4]. The basic principle of IPT can be used in many other situations where contactless power supplies are required.

Although a lot of research work has been undertaken on modeling and design of IPT systems for high power applications at Watts to kilo Watts level [5-12], not much has been reported on design of wireless power systems at very low power level. This research is about the application of IPT in computer mice with power consumption at mW level. The input power is strictly limited by a standard USB power capacity, and the circuit size has to be very small. Cutting the tail off a computer mouse makes it much more convenient to use. However, most existing commercial wireless computer mice are battery powered. The batteries require regular replacement, which creates three obvious problems: the inconvenience of battery replacement, the long-term battery replacement costs, and the environmental concerns associated with battery disposal. Therefore, it would be ideal if the batteries can be eliminated. An additional advantage of a wireless mouse without batteries is it would be lighter in weight. This paper proposes a wireless battery-less computer mice solution, and presents the design and practical implementation of a wireless computer mouse prototype with a super capacitor energy buffer.

II. O VER V IEW OF THE P ROPOSED IPT C OMPUTER M ICE

A.System Configuration

The configuration of the proposed IPT wireless computer mouse is shown below in Fig. 1. As can be seen, the IPT primary circuit and the wireless receiver module were located together to form a single integrated mouse-pad solution. The mouse-pad was then connected to a standard USB port, which provided power and the communication channel with the computer. This architecture was built on top of a commercial battery powered wireless computer mouse, with the original RF hardware replaced by a pair of Nordic nRF24E1 RF transceiver such that the receiver could be integrated with the IPT primary module. The primary track was formed to cover the area of a standard mouse-pad, providing a magnetic field distribution over it. Finally, the pick-up and the wireless transmitter are located within the

battery compartment of the wireless mouse.

Fig. 1: The proposed configuration of a wireless computer mouse.

B.Design Objectives /Requirements

The design objective is to produce sufficient power at the pick-up for the load, which is the wireless computer mouse. According to the specification of the original wireless computer mouse, the power demand is shown in Table I.

Table I: Estimated power consumption of wireless computer mouse Active State Stand-by State

3.3 V x 50mA = 165mW 3.3 V x 33mA = 108.9mW

However, this does not take into account of the wireless receiver module, the losses in the power converter, primary track and the rectifier. This is one of the major design

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